On Thursday, February 28, 2013 3:44:37 PM UTC-5, Bill D wrote:
When Klaus Ohlmann was in Colorado a year so so back he mentioned the N4D he flew to his distance record in 2003 had been "altered" by the factory to allow higher IAS at high altitudes. At the 2012 SSA convention in Reno, I asked Tilo Holighaus what Klaus was talking about.



His answer was they had taken another look at the N4D engineering and flight test data and decided the IAS altitude limitations could be eased. Apparently, Ohlmann's "alteration" was an edit to the Approved Flight Manual.



That said, there are airframe modifications which 'might' improve flutter resistance in the flight levels. Silicon oil filled hydraulic dampers installed as near as possible to the control surfaces are one possibility. Essentially, one pays the price of 'stiffer' controls in exchange for a greater flutter margin. Of course, that does nothing for airframe flutter which does not involve control surfaces.




There were some very good discussions on flutter margins, IAS, and altitude in Homebuilder's Hall articles from the 1970s or 1980s. Searching the SSA Archive will certainly turn them up. There are some commonly used rules of thumb along the lines of x% reduction per thousand feet, but they may not be good enough for the situations you're talking about (i.e. 2% per thousand feet at 50,000 feet is...)

P3